A barium titanyl salt represented by barium titanyl oxalate is used as a raw material for barium titanate used mainly for a piezoelectric material, a semiconductor material, a dielectric material, a laminated ceramic condenser material, a sensor, and so on. In the barium titanate for these uses, it is required that this be microparticles and that the ratio of barium (Ba) to titanium (Ti) contained the barium titanate (mol ratio) be kept uniform (Ba/Ti is about 1).
As to the method for producing barium titanate, there may be mentioned, for example, a solid phase method typically represented by the method in which barium titanate is obtained by heat treatment of a powder mixture of titanium oxide and barium carbonate, a hydrothermal synthesis method as described in Patent Document 1, and a sol-gel method in which hydrolysis of alkoxides of barium and of titanium is used. However, from view of the production cost and energy, a method in which barium titanate is synthesized by heat treatment of the foregoing barium titanyl salt is general, wherein the oxalate method in which barium titanyl oxalate (barium titanyl oxalate salt) is used as the barium titanyl salt as shown in Patent Document 2 is the most general from view of the production cost and availability of the raw materials thereof.
Generally, however, in the case when barium titanate microparticle is synthesized by the oxalate method, because barium titanyl oxalate, which is a precursor to barium titanate, is in the form of coarse particles, a pulverization process is necessary to change it to microparticles; as a result, in many cases, the barium titanyl oxalate microparticle thus obtained hardly shows crystallinity. The barium titanate obtained by burning the barium titanyl oxalate like this readily becomes a coarse barium titanate again, and on top of it the ratio between the barium and the titanium contained therein becomes uneven or inhomogeneous in entirety of the barium titanate powders in a certain instance.
Applicant of the present invention provided a method for producing microparticles, wherein microparticles are separated in a thin film fluid running between processing surfaces which are disposed in a position they are faced with each other, as shown in Patent Document 3; but a method for producing the barium titanyl salt having a controlled ratio between the barium and the titanium had not been disclosed specifically.